Phenotype and physiological responses of P. massonianaseedlings to various Ca levels
As shown in Figure 1A, under low Ca condition, significant withering and necrosis, and collapsed lesions were observed in the needles of P. massoniana compared with medium Ca level, indicating Ca deficiency resulted in the inhibition of needles growth and development. High Ca treatment significantly alleviated this situation as dark green needle colour and fatter needle morphology showed the flourish growth of needles with adequate Ca supply. The decreased total leaf chlorophyll content (Figure 1B) and Pn (Figure 1C) under low Ca treatment, especially the sharply reduced Pn (approximately 50% reduction), suggested photosynthesis was suppressed by Ca deficiency. Under high Ca level, these two parameters recovered and appeared even a little higher than medium Ca level.
There was only a little decline trend in the leaf Ca content under low Ca level, while the leaf Ca content almost doubled when supplying sufficient exogenous Ca (Figure 1D), which is an interesting phenomenon. As to the biomass analysis (Figure 1E), the changing patterns showed similar trend with that in photosynthesis parameters. Ca deficiency reduced soluble protein content while high Ca treatment led to enhanced soluble protein content (Figure 1F), suggesting environmental Ca level influenced protein turnover significantly in P. massonianaseedlings.
Three redox response related parameters including H2O2 content (Figure 1G), total APX activity (Figure 1G) and SOD activity (Figure 1I) were determined. As the result shown, these three parameters exhibited a little decrease at low Ca level compared to the control. However, high Ca treatment induced a slight increase of H2O2 content, total APX activity and SOD activity.